It is known that copolyamides containing from 80 to 20% by weight of the basic unit lauriclactam and, accordingly, 20 to 80% by weight of the basic units of one or more other polyamide-forming substances, can be used for the production of shaped articles of high bond strength at elevated temperature which are suitable for heat-sealing (DAS 1,253,449). It is particularly preferred to use for this purpose copolyamides of lauriclactam and, preferably, caprolactam and/or hexamethylene diamine adipate or hexamethylene diamine sebacate.These known copolyamides into which two or three polyamide-forming monomers are incorporated by condensation as basic units, are widely used in the garment industry for heat-sealing textiles, especially woven fabrics. Unfortunately, the copolyamides described in DAS 1,253,449 have a relatively high melting point which is above about 110.degree.C, with the result that they cannot be used for heat-sealing temperature-sensitive substrates such as leather, temperarture-sensitive natural and/or synthetic woven fabrics, non-woven fabrics, felts, tufted fabrics and the like. Substances with melting temperatures of below about 115.degree.C, if possible below 110.degree.C or even below 105.degree.C, are required for heat-sealing temperature-sensitive substrates of this kind.